Some known vehicle suspensions have stabilizers, each of which is designed to exert a torsional force for reducing a stroke difference between left and right suspensions (specifically, between front left and right suspensions and also between rear left and right suspensions) to limit roll motion of the vehicle at the time of turning the vehicle. With such suspensions, the roll rigidity is increased, so that the roll motion of the vehicle at the time of turning is limited.
In order to increase the degree of limiting of the roll motion, it is conceivable to use the stabilizers, which show the large torsional force against the stroke difference between the left and right suspensions (hereinafter, referred to as the anti-roll effect). However, in a case where the stabilizers, which show an excessively large anti-roll effect, are adapted, the above torsional force is exerted even when the stroke difference between the left and right suspensions is generated due to presence of bumps on a road surface at the time of driving straight-ahead on, for example, a rough road. As a result, there is implemented an effect, which is similar to an effect of increasing a spring constant of a spring of each suspension that supports the vehicle body, so that ride feeling of an occupant(s) is deteriorated. In other words, the ride feeling of the occupant(s) is deteriorated during the time of driving the vehicle, particularly, in the straight-ahead driving state.
Thereby, it is demanded to adapt the stabilizers, which do not show the large anti-roll effect to maintain the good ride feeling of the occupant(s) in the straight-ahead driving, and which effectively limit the roll motion of the vehicle during the turning. In view of this, for example, it is conceivable to adapt the stabilizers, which can vary the degree of the anti-roll effect. The stabilizers, which can vary the degree of the anti-roll effect, are disclosed in, for example,
Japanese Unexamined Patent Publication No. S63-28709 and Japanese Unexamined Patent Publication No. H07-266836.
However, in Japanese Unexamined Patent Publication No. S63-28709 and Japanese Unexamined Patent Publication No. H07-266836, in order to change the degree of the anti-roll effect of the stabilizers, a dedicated mechanism needs to be provided to the suspensions. This may result in an increase in the manufacturing costs, deterioration of mountability of the system on the vehicle and deterioration of the manufacturability of the system.